The invention concerns the construction of devices for the dynamic excitation of panel loudspeakers, particularly the connection of drivers to the acoustic panel in panel loudspeakers which operate according to the bending wave principle.
Sound reproduction devices which operate according to the bending wave principle are known in the state of the art. Such devices, which are also called multiresonance panel loudspeakers, are essentially composed of an acoustic panel and at least one drive system in the form of a driver, where the acoustic panel is made to vibrate when electric sound signals are sent to the drivers. It is characteristic for such sound reproduction devices that a xe2x80x9cbending wave radiationxe2x80x9d becomes possible from a critical lower cut-off frequency, where the bending waves in the plane of the respective panel lead to a sound radiation with a frequency-dependent direction. In other words, a cut through an established directivity diagram shows a principal lobe whose direction is frequency-dependent. These relationships apply to endlessly expanded panels, while the relationships of the multiresonance panels treated in this application are clearly more complex because of the strong edge reflexes. This complexity of multiresonance panels comes from the fact that the cited principal lobe is superimposed by a number of other such principal lobes in a frequency-dependent direction, so that a widely fanned out directivity diagram is created which is also very frequency-dependent. But the multiresonance panels treated here have in common that their directivity diagrams on the average point away from the mid-perpendicular. This behavior causes the room to be more involved in the sound wave projection.
The acoustic panel is constructed according to the sandwich principle, where each of two superimposed surfaces of a very light core layer are connected to a thin cover layer, for example by bonding. For the acoustic panel to have good sound reproduction characteristics, the material of the cover layer must have an especially high dilatational wave speed. Suitable materials are for example thin metal foils or also fiber-reinforced plastic foils.
Special demands are also made on the core layer. It is therefore necessary for the applicable materials to have low mass density and low damping. The core layer materials must furthermore have as high a shear modulus as possible, vertically to the surfaces which are connected to the cover layers. Finally it is necessary for the materials to be used as core layers to have a very low modulus of elasticity in the direction in which the core layer made of these materials has its greatest expansion later on. These two premises, which at first sight seem to be contradictory with respect to the last two requirements, are best fulfilled by a core layer with a perforated structure of openings that preferably have a small cross section, located between the two surfaces provided with the cover layers. In addition to the core layer with the perforated structure, rigid foams can also be used as core layer materials, because they still have suitable shear and elasticity moduli in spite of their isotropic material characteristics. In this connection it must also be mentioned that when rigid foams are used as the core layer material, the cover layers must provide the required anisotropic behavior of the acoustic panel.
In order to radiate sound waves by means of an above described acoustic panel, it is necessary to connect the acoustic panel to at least one driver, which then produces vibrations in the acoustic panel vertically to the plane of the cover layers by means of time-variable power effects. To that end the state of the art generally uses electrodynamic drive systems such as are also used in principle to drive conventional loudspeakers. The drivers are usually equipped with corresponding braces so that these drive systems produce the necessary deformation of the acoustic panel to create bending waves. These braces can be formed for example by a support structure which is arranged at a distance from one of the two cover foils and contains the drive systems. Aside from the fact that such a support structure not only increases the structural depth and the weight of such devices, these support structures also require a considerable production effort. It can therefore be envisioned to directly connect the support structures, which are used as braces for the drive systems, to the acoustic panel. However it is a disadvantage that the support structures connected to the acoustic panel make the generation of bending waves more difficult due to unfavorable changes in the spot impedances.
The object of the invention is therefore to present a panel loudspeaker or better yet a holder for drivers of multiresonant panel loudspeakers, which are connected to the acoustic panel but do not, or only insignificantly, impede its deformation despite the connection to the acoustic panel.
This object is achieved by a device for the dynamic excitation of panel loudspeakers with an acoustic panel which comprises a core layer and at least one cover layer, with at least one electromagnetic driver which has a magnet system, and a holder which connects the driver to the acoustic panel, wherein a ring made of an elastic material is provided as the holder of the respective driver, which concentrically surrounds the magnetic system and is connected thereto, and the ring is arranged in a tube and is connected thereto, while the tube in turn is connected to the acoustic panel.
If the holder of the respective driver is connected in at least three places to the acoustic panel, on the one hand the driver is attached to the acoustic panel, and on the other the free mobility of the acoustic panel is considerably improved, in contrast to the otherwise usual or imaginable connections. Four or more places whereby the driver is connected to the acoustic panel lead to more extensive damping even though better mobility is still provided, compared to conventional connections.
The same result is obtained when the driver is connected to the acoustic panel with a holder containing an elastic member, since this type of connection also ensures that the bending waves which are impressed by the driver on the acoustic panel are able to propagate freely therein.
It is particularly advantageous when the holder, which is only connected at three points to the acoustic panel, is additionally equipped with elastic members, because these strengthen the decoupled connection between the driver and the acoustic panel, since low frequency tuning is required in all cases, i.e. the lowermost natural resonance of the system""s driver plus holder must clearly be lower than the lowest (reproduced) frequencies of interest.